This invention relates to a bushing seal for use in a fluid-to-fluid shaft seal assembly and, in particular, to a shaft bushing seal arrangement for establishing a positive sealing interface between a sealing fluid and the working fluids contained within a rotary machine.
As disclosed in U.S. Pat. No. 3,695,621, to Damratowski, one prevalent method of sealing a shaft contained within a rotary machine against leakage is to provide a fluid sealing assembly between the shaft and the casing or end wall of the machine. The assembly basically includes a first shaft bushing confronting the working fluids contained within the machine and a series of pressure breakdown bushings aligned behind the front bushing. A high pressure sealing fluid is brought into contact with the shaft within the front bushing region to establish a fluid interface capable of preventing the working fluids from escaping from the machine. The pressure in the sealing fluid is periodically reduced or broken down as the fluid moves along the shaft beneath each of the breakdown bushings toward the low pressure side of the assembly. As can be seen, it is important in this type of sealing arrangement to establish a continuous and positive sealing interface at the front bushing to insure efficient seal performance.
Establishing and maintaining such a positive fluid-to-fluid interface has long been a problem in the art. Two primary factors are believed to contribute toward seal failure. The first involves the inability to properly mount and maintain the front seal within the assembly. The second factor is attributed to the incomplete formation of a fluid sealing barrier between the front seal and the shaft. The present invention is directed toward overcoming these shortcomings found in the art.